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What green tea extract may actually do
I get asked all the time about weight loss supplements: do any of them work? There are really two problems with most weight loss supplements. The first, and most concerning from a drug interaction standpoint, is that because the supplement industry is not regulated by the Food and Drug Administration (FDA), you can not be certain what any supplement pill actually contains.
Taking Weight Loss Supplements Could Backfire
Losing weight is not easy. Even for those who don't have significant obstacles to weight loss, like those taking certain medications or with certain conditions, it takes a certain amount of discipline to watch portion size, make healthier choices (most of the time), and exercise faithfully. So I understand why people want to take weight-loss supplements.
The Evidence for Weight Loss Supplements
With the number of overweight and obese adults in the United States estimated to be over 2/3 of the total adult population, it's no surprise that in 2010 US consumers spent an estimated $2.4 billion on weight loss supplements and meal replacements. And it's not all that unusual to be using them, either: in 2008 about 1 in 3 overweight or obese people admitted to at least trying them.
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Back in 2012 I reported on an article that was a thorough review of the state of the evidence for herbal weight loss supplements, including ephedra, green tea extract, and chromium picolinate. While the author concluded that further research was warranted on green tea extracts, none of the other herbal supplements she covered appeared to be both effective and safe.
Here we are, almost eight years later, and people are still using herbal supplements to try to lose weight. In a recent article in Diabetes, Obesity & Metabolism (2020;1-13), a team at the University of Sydney, Australia published a review and meta-analysis of randomized, controlled trials of herbal weight loss supplements.
The authors searched the literature to find all randomized, controlled trials published before August 2018 comparing an herbal weight-loss supplement with placebo and performed with healthy, overweight or obese adults as participants. The authors conducted meta-analyses for those supplements with at least 4 studies and designated a change in weight of at least 2.5 kilograms (about 5.5 pounds) as clinically significant.
As part of their analysis, the authors evaluated the quality of the studies themselves, asking such questions as:
These are just a sample of the different herbal supplements included in the studies:
A meta-analysis of 5 studies that utilized green tea in combination with other herbs found a statistically significant weight loss of about 1.6 kilograms (about 3.5 pounds), but this did not rise to clinically significant. The studies utilizing green tea alone, however, showed no more weight loss than placebo. Unfortunately, none of these studies reported their trial design and procedures adequately to allow the authors to assess the risk of selection bias, while other studies were considered to be at high risk of bias because the authors worked for the company owning the supplement tested.
A meta-analysis of five studies that looked at garcinia administered as a single herb showed "a non-significant effect on weight" - and so did a meta-analysis of 6 other studies that utilized garcinia in combination with other herbs. These also were poorer quality studies, with five published studies going so far as to avoid reporting absolute values and instead using graphs showing change from the start of the study to the end of the study. (Imagine a graph with no numbers!)
Administered as a single herb, a meta-analysis of 5 studies showed statistically but not clinically significant changes of about 1.6 kilograms (3.5 pounds) as compared to placebo, while combination preparations had a slightly greater effect (1.8kg). As the authors described them: "a lack of detail in trial design and methodology was common across the studies," making it difficult to adequately assess the quality of the study.
Only one of 3 studies found reported a clinically significant weight loss of about 4.8 kg (about 10.6 pounds), but this was a combination preparation. All three studies failed to adequately describe the amount of the test supplement administered or did not appropriately describe the results. Once again, two of the studies only reported results in unlabeled graphs.
The authors state, "The results need to be interpreted cautiously as nearly all [randomized controlled trials] included in this review were found to be at high risk of bias in at least one [area]...."
While some herbal preparations may well assist in weight loss, we still don't have any good data to show which ones work, how much one should take, and whether they are safe. Save your money and stick to what we know will work to improve your overall health: improving the quality of what you eat and getting enough sleep and exercise.
First posted: March 25, 2020